1. Field of the Invention
The present invention relates to a display apparatus using a liquid-crystal panel, and more particularly to a display apparatus having a configuration capable of further realizing reduction in thickness and border width of the apparatus.
2. Description of Related Art
A display apparatus using a liquid-crystal panel includes a light source, and also includes an optical sheet for diffusing or condensing light from the light source between the light source and the liquid-crystal panel. For a light source in a recent display apparatus, in order to reduce the thickness of the display apparatus and to suppress unevenness in luminance, an edge light type is frequently used in which multiple light emitting diodes are so arranged to be opposed to an end surface of a transparent plate referred to as a light guide plate, and light entering from the end surface is uniformly emitted from a wide surface.
While a light guide plate made of the same glass material as that for the liquid-crystal panel may sometimes be used, a light guide plate is often made of resin such as PMMA (Poly (methyl methacrylate)) or MS, which has a relatively low rigidity compared to glass. Moreover, the optical sheet is a flexible film such as PET (Polyethylene terephthalate). It is thus necessary, for positioning a light guide plate and an optical sheet with a liquid-crystal panel, to prepare a holding member made of resin or metal, which is more rigid than the materials used for those to be positioned.
Furthermore, the light guide plate and optical sheet have relatively high coefficients of thermal expansion, which causes wrinkles or deflections particularly because the optical sheet is a film. The wrinkles or deflections in the optical sheet cause defects such as unevenness or lowering in luminance of the display apparatus. The holding member for the light guide plate and optical sheet requires a holding structure for positioning and holding the optical sheet with a margin for possible expansion in consideration of thermal expansion.
A conventional display apparatus having such a holding structure is now described.
FIG. 8 is a cross section schematically illustrating the main parts of a conventional display apparatus 90. The display apparatus 90 includes a liquid-crystal panel 91, a light source device 92 and an optical sheet 93, as well as holding members 94, 95 for the components described above.
The liquid-crystal panel 91 is a display panel and has the shape of a rectangular flat plate. The liquid-crystal panel 91 is so configured that liquid-crystal 913 is injected between two glass substrates 911 and 912 which are arranged to be opposed to each other with a predetermined distance therebetween, and is sealed by seal materials 914 and 915. On the glass substrates 911 and 912, various elements including an electrode for driving the liquid-crystal 913 are formed (not illustrated). The liquid-crystal panel 91 includes, at an end on one long side of the glass substrate 912, a drive circuit (driver) 916 connected to each element at an end on one long side of the glass substrate 912, and a substrate 917 supplying signals to the drive circuit 916.
The light source device 92 is a light source of the edge light type using a light emitting diode 921. The light source device 92 is so configured that multiple light emitting diodes 921 are arranged on a long and narrow substrate 923 located along an end surface on the long side of the light guide plate 922, which is made of resin with high transparency such as acrylic and is formed to have the shape of a rectangular flat plate, to be opposed to the end surface. The substrate 923 is connected to a heat sink 924 for dissipating heat generated by the light emitting diodes 921. The cross sectional shape of the heat sink 924 is an L-shape, the vertical line thereof positioned along one wide surface of the light guide plate 922 whereas the horizontal line thereof positioned along an end surface on the long side of the light guide plate 922. On one wide surface of the light guide plate 922 on the side along which a part of the heat sink 924 is located, scattering dots 925, which irregularly reflect and deflect the light traveling in the light guide plate 922 and reaching the one wide surface side and guide the light to another wide surface side, are formed by printing or laser machining.
The components of the light source device 92 are positioned by the holding member 94. The holding member 94 is, for example, made of metal, and has the shape of a rectangular box with one surface being open and a side plate on one long side thereof further being open. The bottom surface of the holding member 94 is a little larger than the dimension of the wide surface of the light guide plate 922, and the height of the side plate is a little larger than the thickness of the light guide plate 922. A reflection surface of the reflection sheet 926 is adhered to one wide surface of the light guide plate 922 where the scattering dots 925 are formed. The light guide plate 922 is placed on the holding member 94 such that the side of the reflection sheet 926 is opposed to the bottom surface of the holding member 94. The light emitting diode 921, substrate 923 and heat sink 924 are placed on one long side at which the side plate of the holding member 94 is opened. Here, the heat sink 924 is so placed as to sandwich the reflection sheet 926 and the bottom plate of the holding member 94 between the light guide plate 922 and a part of the heat sink 924 located along the wide surface of the light guide plate 922. Thus, the light source device 92 is formed, in which the light from the light emitting diode 921 enters the inside of the light guide plate 922 from the side surface of the light guide plate 922, and travels inside thereof while partially being reflected on different surfaces or totally being reflected by the reflection sheet 926, and is emitted from a wide surface of the light guide plate 922 opposite to the side of the reflection sheet 926 due to scattering by scattering dots 925. Accordingly, uniform planar light is emitted from the wide surface of the light guide plate 922 to the liquid-crystal panel 91 side.
The optical sheet 93 has a shape of a rectangle, which is an optical sheet group including three sheets of, for example, a lens sheet 931, a prism sheet 932 and a diffusion sheet 933.
The liquid-crystal panel 91 and optical sheet 93 are positioned with respect to the light source device 92 by the holding member 95 which is fitted with the holding member 94. The holding member 95 is, for example, a frame body made of resin, and is so configured that a circumferential groove is formed at the outer peripheral edge on one surface thereof and the side plates of the holding member 94 are fitted into the groove. Moreover, a receiving part for positioning the optical sheet 93 is provided at the inner peripheral edge on the other surface of the holding member 95. The receiving part has a depth a little larger than the thickness of the optical sheet 93. Furthermore, the outer peripheral edge on the other surface of the holding member 95 corresponding to the opposite side of the groove configures a protrusion circumferentially formed to correspond to the receiving part of the optical sheet 93. Parts of three side plates of the holding member 94 and the heat sink 924 are fitted into the groove of the holding member 95 as described above. It is so configured here that the inner peripheral edge on one surface of the holding member 95 presses against the circumferential part of the light guide plate 922 via a spacer 951. On the other surface of the holding member 95, the optical sheet 93 is so placed that the circumferential part of the optical sheet 93 is in contact with the receiving part. Next, the liquid-crystal panel 91 is placed on the holding member 95 via the spacer 952 such that the outer peripheral edge of the glass substrate 912 of the liquid-crystal panel 91 corresponds to the projection on the above-described other surface of the holding member 95. Here, the liquid-crystal panel 91 is so placed that the side of the drive circuit 916 and the substrate 917 corresponds to the side of the light emitting diode 921 of the light source device 92. Accordingly, the liquid-crystal panel 91 and optical sheet 93 are positioned with respect to the light source device 92, which forms the display apparatus 90.
As described above, in the conventional display apparatus 90, thinning of the apparatus is insufficient because of the thickness of the holding members 94 and 95, and the narrowing of border width is also insufficient because the holding members 94 and 95 are larger in plane direction than the liquid-crystal panel 91 and light guide plate 922. To address this, a configuration for realizing reduction in thickness of an apparatus having a small display panel, such as a mobile phone, is disclosed.